1. Field of The Invention
The present invention generally relates to an apparatus for controlling operating pressure during predetermined increments of time in a mold cycle for producing intricate, and/or thin walled parts within a cyclical injection molding die operatively associated with an injection molding machine.
Injection molding of plastic parts in an injection molding machine has been in wide use throughout the world for the past three decades, and is presently one of the most commonly used ways of rapidly fabricating complex plastic parts in large quantity. There is an increasing need to produce plastic parts with greater tolerance control, better quality and with increased production rates to comply with ever increasing demand. This means that it is essential to eliminate any potential loss of parts in the molding process due to gas burns and imperfect surface detail. In addition, there is an increasing need to mold highly complex and intricately detailed parts having critical tolerances and otherwise perfect detail for medical and electronic applications. For example within the medical field, maintaining very critical tolerances with absolutely no imperfections is essential with certain highly detailed, and thin walled parts.
The present invention has been developed to provide such intricate parts through application of an apparatus which eliminates blemishes, gas burns, voids and other imperfections present in the injection molding process's known to date. There is included with the present invention an apparatus which virtually eliminates reject parts through a novel process which divides up the mold cycle in increments with varying degrees of applied vacuum and positive air pressure applied to the mold cavity under predetermined lengths of time.
2. Description of the Prior Art
The idea of applying a vacuum by means of a vacuum pump or vacuum reservoir to a mold cavity is not new. For example, there is a U.S. Pat. No. 4,412,804, issued to Huther on Nov. 1, 1983 which demonstrates how to utilize a vacuum source, as connected to the mold cavity of an injection molding die for forming ceramic parts. This patent teaches that it is possible to have a vacuum source 100 to 1000 times greater than the volume of the mold, and to have a closed-circuit evacuating system to achieve production of precision parts of ceramic material. The ceramic parts having more uniform composition by removing air bubbles present in the molten material through the application of the vacuum.
While the above named patent reaches toward the production of ceramic parts having increased perfection, it is not demonstrated in the patent how to maintain the mold clean, prevent distortion of the parts during ejection from the mold and to provide high production runs of highly intricate and thin walled parts such as those previously described in the field of the present invention. It is for this reason that the present invention is provided, and will teach what has not been done heretofor.